A good old-fashioned carpenter/joiner could knock you some blocks up in any timber you could name. Take one of the originals with you though so he can measure it and examine it for patina (which he may be able to match with dye and wax).

I have just, after 12 months, laid my hands on some old Imperial sized parquet finger blocks. The only way to source these (unless you get a chippy to knock some up for you) is to regularly contact all architectural salvage suppliers and hope they will come up trumps.
The major problem nowadays seems to be that old floors are not removed, merely gobbled up by a floor cruncher and disposed of. Time = money = profit rules all.